Method of making tubular axles



Patented Mar. 9, 1943.

METHOD or Mame. 'ruunsn AxLEs Donald E. BaboocbPittsbm-gh, Pa., assigner to Pittsburgh Steel Company, Pittsburgh, Pa., a.

vanta corporation of Pennsyl application september 12, 1940, serialize. 356,416

(o1. ca -165) 1 Claim.

This invention relates to tubular axles for railway cars. The principal place of failure of railway car axles is at the inner ends of the wheel seats because it ls at those points on the outer surface of the seats that the maximum stress concentration occurs. I have found that the principal reason for this is that the distribution of metal and the internally combined stresses are of such nature that they cause the highest tension and compression stresses resulting from the bending of the axle in use to concentrate or localize in tion into the wheel seats in such a manner that .the tension resulting from the'bending is applied to the seats in 'a direction parallel to the tube axis, rather than at an angle thereto. This reduces the stress concentration that would other- Wise develop on'the outer surface of the wheel seats in those areas most subject to fatigue failure.

those areas. Various ways have been proposed I for increasing the fatigue strength of axles, and

although some progress has been made, considerable work in this direction has remained to be done. -v

It isamong the objects Vof thisinvention to The invention is illustrated in the accompany# lng drawing in which Fig. 1 is a side view, partly in section, ofmy axle just after its ends have been upset; Fig.l 2 is a view similar to Fig. 1 showing the axle just after the ends have been forged; Fig. 3 is anenlarged fragmentary section of an end portion of theaxle sh'owing in an exaggerated manner the effect of tension orv 1 bending stresses on the wheel seat; and Fig. 4 is provide a railway car tubular axle which is light f in weight, which has greater fatigue strength than any known heretofore, and which can be` readily manufactured. Another object is to provide a method of making such an axle.

I'In accordance with thisinvention the end portions of a thin wall tube are heated and then necessary for the central portion of a railway car upset axially. The metal is allowed to flow radially inwardly, whereby the walls of the upset' "portion are thickened in order to i'orm wheel seats and .ioumal bearings. The central portion of the tubeis not upset or otherwise altered but retains the uniform diameter and wall thickness of the original tube. During the upsetting the dies I.

k2 is forced into the end of the tube in order to 3o' bearing-forming portions of the tube may or may not be thickened and held to their original outside diameter, depending on thev design o f the dies, but the outer diameter of the seat-forming portions is allowed to increase in order to form raised wheel seats whose mean diameter at any point along their length is greater than the mean diameter of the central portion of the axle'. After the upsetting operation the bearing-forming portions of the tube are forgedr without interior support to reduce vtheir outer diameter and to form flanges on their outer ends. Due to the wheel seats being raised in this manner and a fragmentary longitudinal section showing a modified lform of the axle after upsetting by modiiled dies. 1 4

Referring to Fig. 1 ofthe drawing. a tube of uniform diameter from end to end and having a wall thicknessv substantially Vno greater than is axle has only its end portions heated to a uniform temperature gradient. After an end has been heated, it is'immediately gripped by upsetting At the same moment a tapered mandrel upset it. As the mandrel is smaller than the opening through the tube, and as the dies limit the flow of metal radially outwardly, the hot metal is forced to. flow inwardly around the mandrel and thereby thicken the wall of the upset end portion of the tube'so that wheel seats and journal bearings ofthe necessary increased wall thickness can be formed. By taperingo the temperature between the wheel seats and connected by a central portion of the axle which has a uniform outside diameter throughout its length, the tensional Vand compression stresses which are due to bending of the axle in use cause the maximum .stress concentration along thev inner surfaces of the wheel Vseats with materially ed stress applied or developed in and along Ithe outer surfaces of the seats. The'- bendingstresses are transmitted through the straight cylindrical wall ofthe tubes central por. 55

central portion of the tube. inwardly diverglng surfaces Scan be formed which prevent localization of stresses. at lthese points where the wall thickness changes.

It 1s a feature-or this invention that themes.

are provided witharcuate recessesof a predeter- 'mined depth to permit some of the metal of the tube's end portions to flow outwardly into them to form raised wheel seats 3, and that the' diam. eter of the mandrel is such that the mean diam-- eter of the wheell seats at any point along. their length must be greater than the mean diameter of the straight central portion I of the tube connecting them. vhave this relation of diameters will be explained presently. The upsetting dies may be shaped as shown infix. 1, in which the bearing forming 'I'he reason that it is desirable to.l

portions of the tube are prevented from expanding, or they may be shaped as in Fig. 4 at ia in order to taper the tube ends and thus permit theV outer diameter of the bearing portions to increase.

After the upsetting operation the bearing- 5 forming portion of each end of the tube is forged down by forging dies 6, as shown in Fig. 2, in order to decrease it to a size suitable for a journal bearing 1 having a mean diameter less than that of central portion 4, and to form a flange 8 on its outer end. If wheel seats 3 formed in the upsetting operation are the correct finish size, they will not be affected during this forging operation. But if they are initially made oversize, they will be forged down to correct diameter at this time.

Another feature of this invention is that the central portion l of the axle which` connects the wheel seats remains straight, as distinguished from tapering toward its mid-point. That is, its

wall thickness and outer diameter are uniform throughout its length. As a result of this and the relations of mean diameters referred to above, the tensionand compression that are applied longitudinally to the axle as it is bent under load produce stresses tthat enter the Wheel seat parallel to the tube axis andprincipally inside the limits of the mean diameter `of the seat. This condition is illustrated in Fig. 3 where the horizontal line A represents one end o f the mean is represented by the line B. When tension-is transmitted to the wheel seat by the .tubular wall ofthe axle it vtends to stretch the inner surface of the wheel seat more than the outer surface until the central portion of line B coincides with line A. This causes the wheel seat 44o to bow inwardly, as shown. A change in stress concentration from that present in prior axles 4, is thus 4obtained because it is greater along the inner surface of the wheel seat than the outer,

and it is spread out over those surfaces and 45 tially constant during the upsetting whereby the not localized at the inner end of the wheel seat. It is much more desirable to have this stress concentration along the inner surface of the wheel seat because that surface is free of wheel seat working and other stress raising effects.

such as point contacts, etc.

The completely formed axleis then heated throughout its length, its ends are plugged and it is quenched. This further decreases the exvantage can be obtained in other ways. such as by cold forming or sizing. This is because the hardening by cold working or quenching of any section of steel causes it to expandV and reduces its density. This expansion. if it occurs on one side only of the section, will cause that side to elongate and stretch the opposite unhardened side. A reverse reaction immediately occurs wherein the hardened section is automatically brought under a compressive stress caused as a reaction .to the tension developed in the unhardened surface. The effect of this is to drop the point of maximum tension to a position inside the main body of the metal structure where fatigue cracks can not successfully develop. In a tubular axle, this treatment plays a desirable part by putting compressive stresses on the outside surface of the wheel seat and tensional stresses on its inner surface, thereby increasing the fatigue life of the axle. It ispossible in this manner to put an appreciable stress on the wheel seat before the hardened surface of the seat has been stressed to the point where its fatigue limit is exceeded and failure develops.

According tothe provisions of the patent statutes, I have explained the principle and con-i struction of my invention and have'illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that, within the scope of the ap pended claim. -the invention may be practiced otherwise than as specifically illustrated `and described. L l

I claim:

The method of making a railway car tubular axle, comprising heating substantially uniformly the bearing and wheelseat forming portions only of a thin walled tube of uniform size, lthe central portion of the tube remaining cool and being .connected to the heated wheel seat portions by short portions increasing in temperature axially outwardly, upsetting axially 'on a tapered mandrei the heated portions only to increase their wall thickness, holding the'outer diameter of only said central and bearing portions substaninner surfaces` of said end portions are ccntracted and joined to theinner surface of said central portion by diverglng surfaces and whereby raised wheel seats are formed which arev connected by a central tubular portion cf uniform size, and controlling the outer and inner diam-- eters of said wheel seats during saidv upsetting so that their mean diameter is greater than the tent to which the outer surfaces of the wheel mean diameter cf said central portion.

seats can be subjected to strains. The same ad l DONALD E. BABCOCK. 

